When your CentOS server screams "No space left on device", it's typically /var that's the culprit. Let me walk through a real-world solution approach that's saved me countless times.

# First, verify the actual disk usage
df -h
du -sh /var/* | sort -h

Before MySQL can restart, we need immediate breathing room:

# Clear system logs (preserving current logs)
sudo journalctl --vacuum-size=100M
sudo truncate -s 0 /var/log/*.log

# Clean package cache
sudo yum clean all
sudo package-cleanup --oldkernels --count=1

For persistent solutions, implement log rotation and scheduled cleanups:

# Create a cleanup script /usr/local/bin/clean_logs
#!/bin/bash
find /var/log -type f -name "*.log" -mtime +30 -exec rm -f {} \;
find /var/log -type f -name "*.gz" -mtime +90 -exec rm -f {} \;

Make it executable and add to cron:

chmod +x /usr/local/bin/clean_logs
(crontab -l ; echo "0 3 * * * /usr/local/bin/clean_logs") | crontab -

For MySQL-related space issues:

# Clean binary logs if replication isn't needed
PURGE BINARY LOGS BEFORE DATE_SUB(NOW(), INTERVAL 7 DAY);

# Optimize InnoDB tablespace
mysqlcheck -o --all-databases

Implement these configuration changes:

# /etc/logrotate.conf
/var/log/mysql.log {
    daily
    rotate 7
    compress
    delaycompress
    missingok
    notifempty
}

# /etc/my.cnf
[mysqld]
innodb_file_per_table=1
expire_logs_days=3

For /var/www overflow, consider symlinking to /home:

sudo systemctl stop httpd
sudo mv /var/www /home/
sudo ln -s /home/www /var/www
sudo systemctl start httpd

When standard cleanup isn't enough:

# Find large files
find /var -type f -size +100M -exec ls -lh {} \;

# Monitor disk space in real-time
watch -n 60 'df -h; du -sh /var/* | sort -h'

---

First, let's identify the largest space consumers in your /var partition:

# Find largest directories in /var
sudo du -sh /var/* | sort -rh | head -n 10

From your output, we can see /var/www (2.6G) and /var/lib (1.5G) are the biggest consumers.

For log files (/var/log at 221M), use these commands:

# View largest log files
sudo find /var/log -type f -exec du -sh {} + | sort -rh | head -n 10

# Rotate and clean old logs
sudo logrotate -f /etc/logrotate.conf
sudo journalctl --vacuum-size=100M

# Clear specific application logs
sudo truncate -s 0 /var/log/mysqld.log
sudo truncate -s 0 /var/log/httpd/access_log
sudo truncate -s 0 /var/log/httpd/error_log

The /var/lib/mysql directory often grows large. Try these optimizations:

# Clean up MySQL binary logs (if replication isn't used)
PURGE BINARY LOGS BEFORE NOW();

# Optimize tables to reclaim space (run in MySQL client)
mysqlcheck --optimize --all-databases

# Temporarily move ibdata files if needed (stop MySQL first)
sudo systemctl stop mysqld
sudo mv /var/lib/mysql/ibdata1 /tmp/
sudo systemctl start mysqld

For /var/www (2.6G):

# Find largest files in web directory
sudo find /var/www -type f -exec du -sh {} + | sort -rh | head -n 20

# Clean up temporary uploads and caches
sudo find /var/www -type f -name "*.tmp" -delete
sudo find /var/www -type f -name "*.cache" -delete

# Consider moving static content to /home partition
sudo mv /var/www/static /home/www-static
sudo ln -s /home/www-static /var/www/static

Create a cleanup script (/usr/local/bin/cleanup_disk.sh):

#!/bin/bash
# Rotate logs
/usr/sbin/logrotate -f /etc/logrotate.conf

# Clear package manager cache
dnf clean all || yum clean all

# Remove old kernel versions (keep last 2)
package-cleanup --oldkernels --count=2

# Remove temp files older than 30 days
find /tmp -type f -mtime +30 -delete
find /var/tmp -type f -mtime +30 -delete

# Clean yarn and npm caches
if [ -x "$(command -v yarn)" ]; then
    yarn cache clean
fi
if [ -x "$(command -v npm)" ]; then
    npm cache clean --force
fi

Make it executable and set a cron job:

sudo chmod +x /usr/local/bin/cleanup_disk.sh
sudo crontab -e
# Add this line to run weekly:
0 3 * * 0 /usr/local/bin/cleanup_disk.sh >/dev/null 2>&1

1. Set up monitoring with a simple disk check script:

#!/bin/bash
THRESHOLD=90
CURRENT=$(df /var --output=pcent | tail -1 | tr -d '% ')

if [ "$CURRENT" -gt "$THRESHOLD" ]; then
    echo "WARNING: /var partition at ${CURRENT}% usage" | mail -s "Disk Space Alert" admin@example.com
    /usr/local/bin/cleanup_disk.sh
fi

2. Consider resizing partitions or moving directories to less utilized partitions:

# Example moving MySQL data directory
sudo systemctl stop mysqld
sudo mv /var/lib/mysql /home/mysql
sudo ln -s /home/mysql /var/lib/mysql
# Update /etc/my.cnf with new datadir
sudo systemctl start mysqld